Testis

The testis are ovoid organs responsible for sperm production.

• Tunica Albuginea - capsule of thick connective tissue.
• Seminiferous Tubules - each lobule contains 1 to 4 highly-coiled seminiferous tubules lined by a germinal epithelium that is the site of sperm production.
• Sertoli Cells - large, columnar cells that extend the full thickness of the germinal epithelium.
• Irregular, euchromatic nucleus with a single, prominent nucleolus.
• Blood-testis Barrier - these cells separate the basal epithelial compartment (of spermatogonia) from the luminal compartment (of spermatocytes, spermatids and sperm).
• Spermatogenesis - the process by which spermatogonia develop into sperm. Many dividing cells are seen in the germinal epithelium.
• Spermatogonia - single layer of germ cells resting on the basement membrane.
• Primary Spermatocytes - arise from spermatogonia and cross from the basal epithelial to luminal compartment of the germinal epithelium.
• Secondary Spermatocytes - arise from primary spermatocytes and rapidly divide (rarely visible).

• Spermatids - arise from secondary spermatocytes and undergo spermiogenesis to transform into sperm.
• Small, spherical cells (8 µm or less) with intensely stained nuclei near the lumen.
• Embedded in the cytoplasm of Sertoli cells.
• Sperm - released into the lumen.
• Small, pointed head with a long tail (~60 µm long).
• Leydig Cells (or Interstitial Cells) (#1 and #2) - found in the connective tissue (or interstitium) between seminiferous tubules.
• Large, round cells (20 to 30 µm diameter) with vesicular nuclei and eosinophilic cytoplasm.
• Usually occur in clusters of 5 to 30 cells.
• Secrete testosterone.
• Mediastinum - region in which seminiferous tubules converge and sperm exits the testis.
• Straight Tubules (or Tubuli Recti; #1 and #2) - short, terminal section of each seminiferous tubule lined only by Sertoli cells.
• Rete Testis - straight tubules empty in an anastomosing labyrinth lined by a simple cuboidal or columnar epithelium.